With the recent increase in demand for safe and fuel efficient cars, a need exists for tire rubber materials which simultaneously provide improved properties including mechanical properties, abrasion resistance, and fuel economy. Several techniques have been proposed to solve this challenge, such as use of diene polymers with low heat build-up properties, use of silica as filler for reducing heat build-up, use of fine particle carbon black having high reinforcing properties and excellent abrasion resistance, and combinations of these techniques.
For example, it is contemplated that the fuel economy and abrasion resistance of rubber compositions may be further improved by combining a rubber component having an increased molecular weight with filler to increase their affinity. However, since rubber components with an increased molecular weight usually have poor processability, simply combining those components will result in deterioration of processability of the rubber composition due to its increased viscosity. This can cause silica or fine particle carbon black to have poor dispersibility, and it is therefore difficult to achieve a good balance of sufficient properties.